It is known to use internal olefin sulfonates (IOS) as a surfactant for a variety of applications including chemical Enhanced Oil Recovery (cEOR).
Further, it is known to prepare olefin sulfonates from alpha-olefins and internal olefins, by sulfonating the olefins, for example by contacting with sulfur trioxide as the sulfonating agent. This is followed by neutralizing and hydrolyzing the sulfonated olefin containing intermediate mixture which comprises alkene sulfonic acids and sultones that are to be converted into the desired sulfonates. Said neutralization step and subsequent hydrolysis step both comprise contacting sulfonated olefin with a base containing solution, for example an aqueous NaOH containing solution. The hydrolysis step is generally carried out at a higher temperature than the temperature in the neutralization step, and is aimed at completing the reaction of the base with sulfonated olefin. See for example Adami, “The Production of α-Olefin Sulfonate by SO3 Sulfonation”, Section 5.3.1, pages 102-109, Handbook of Detergents, Part F: Production, CRC Press, 2009.
Further, EP0351928A1 discloses a process for the preparation of internal olefin sulfonates which comprises reacting in a film reactor an internal olefin having from 8 to 26 carbon atoms with a sulfonating agent, in a mol ratio of sulfonating agent to internal olefin of 1:1 to 1.25:1 while cooling the reactor with a cooling means having a temperature not exceeding 35° C., and allowing to neutralize and hydrolyze the reaction product from the sulfonation step.
More in particular, in Examples 1-7 of EP0351928A1, a sulfonation process was carried out wherein a mixture of C13-14 internal olefins was contacted with sulfur trioxide in a stainless steel reactor tube. The reactor tube was cooled by flowing water of low temperature along the outside of the reactor tube in a direction opposite to the direction of the feed/SO3 stream through the reactor tube. In Examples 1-4, the cooling water had an inlet temperature of 8° C. and an outlet temperature of 13° C. In Example 5, the cooling water had an inlet temperature of 10° C. and an outlet temperature of 15° C., while in Examples 6 and 7 the inlet temperature was 12° C. and the outlet temperature 17° C. That is to say, the above cooling water inlet temperatures are relatively far below the maximum of 35° C. taught in EP0351928A1. Indeed, EP0351928A1 discloses a preference for the cooling means temperature of only 0° C. to 25° C. Further, it is described that depending upon the circumstances even lower temperatures may be used. That is to say, the use of higher temperatures is not suggested at all in EP0351928A1.
It is an object of the present invention to provide a process for preparing an internal olefin sulfonate which process is suitable for preparing the sulfonates from internal olefins having an average carbon number that is equal to or greater than 20. A further object of the present invention is to provide internal olefin sulfonates, made from such internal olefins having an average carbon number that is equal to or greater than 20, that are suitable to be used as a surfactant in chemical Enhanced Oil Recovery (cEOR).